CI Improvements

### A collection of tasks that would make CI more effective

- [ ] Rust tests can be skipped if a commit only touches README files
- [ ] Rust tests should run `clippy` and `rustfmt`
- [x] ~Rust tests should cache dependencies, and build artifacts if possible~ Fixed by eb3d06f
- [ ] Rust tests should run on `wasm` toolchains in addition to `x86_64`